Focal populations may be 'farmed' rather than preyed upon. Cows turn hay and feed into meat and milk, of interest to the farmer who maintains the animals in such a way as to minimize energy expenditure in exercise and aggression. Placid cows are more efficient but the entire situation in which humans do part of the work of maintenance of the population is highly unnatural.
In a farming situation, the consumption and the yield from a focal population can be measured in units of money and time. The ratio of price of produce to cost of husbandry is important, but since it is not defined in energetic terms it is not an ecological efficiency. Recall that part of the motivation of Lotka, Lindeman, and Hutchinson was to make theoretical contact with thermodynamics.
Ecological efficiencies in the sense of Lindeman, used in most ecological literature, do not have any meaningful definition for entire communities or entire ecosystems. There is a tendency to confuse the ideas of efficiency and effectiveness.
Geese can eat grass off golf courses, birds may eat noxious insects, and bacteria can help digest organic matter in sewage effluent. These valuable processes are only remotely connected to ecological efficiency. Advocates for vegetarianism quite correctly note that the amount of resources - sunlight, water, and fertilizers needed to grow animal flesh - is several times larger than that needed to produce an amount of vegetable food of equivalent or superior nutritional quality.
Ecosystems or communities can be managed for particular purposes, for example, maximum steady-state yields of fish, seaweed, grass, elephant tusks, or game. Management can increase these yields, but this is deeply different from ecological efficiency, which cannot be measured for an entire system. Animals and plants can be more or less effective at performing desired functions. Effectiveness at particular processes is ofimmediate intuitive value. It is less obvious why ecological efficiency matters for any practical purpose.
A high ecological efficiency does not imply a large amount of material being maintained at any trophic level.
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